PLEASE HELP!!! (Build Help) Experts...

Ijust finished my build on Sat. night. Everything was all good.

I used an old Windows home edition the next day to upload it and everything was fine again.

Once all done installing drivers i was able to connect it to the internet and then began to install crysis.

After that the intro was playing and i hadn't connected my new g51 sound sys. so i just took some headphones and connected it to the front of the case. AND IT JUST SHUT OFF!!!!

Strange part is the led on the front of the case is still on, small led on the motherboard, and the light to the mouse.

This is my set up:
motherboard-evga 750i ftw
cpu-intel q9400
gpu-gtx 260 xfx black edition
cpu cooler- xigmatek s1283
hd-wd 320g
ram-ocz sli- 4g
sentry lx
psu-corsair psu